Introduction to Modern Dynamics: From Classical Mechanics to Complex Systems offers a comprehensive and unified perspective on dynamics for the 21st century. Now in its third edition, the text provides a rigorous yet accessible foundation in Lagrangian and Hamiltonian mechanics, modernized with a geometric viewpoint that enhances intuitive understanding. The book's four-part structure provides a seamless transition from foundational principles to cutting-edge topics, beginning with the foundations of classical and complex mechanics and moving on to cover applications of those concepts to complex systems, as well as relativity and spacetime. To facilitate student learning and prepare them for careers in research and technology, this edition has a renewed focus on practical application. Each chapter includes numerous worked problems, and online access to computational code allows students to explore a wealth of nonlinear phenomena. These resources are designed to equip students with the analytical and computational skills necessary to tackle the complex dynamical systems that are increasingly central to science and technology, while continuing the tradition of classical mechanics as the common language for practicing physicists.